Device for purifying and/or decontaminating polyester

ABSTRACT

The invention relates to a device for purifying and/or decontaminating polyester, in particular polyethylene terephthalate (PET). Said device has a rotary kiln ( 1 ), which is at least partially heated and fed with a mixture of polyester and an alkaline material, for carrying out a saponification reaction in the mixture. The invention is characterised in that the rotary kiln ( 1 ) contains a weir-type element ( 22 ), which closes at least part of the interior ( 5 ) of said kiln ( 1 ).

[0001] The present invention relates to an apparatus for cleaning and/ordecontaminating polyester, in particular polyethylene terephthalate(termed PET hereinafter). PET is one of the most used polyesters. PEThas many uses, but is primarily used in the drinks industry as materialfor drink bottles.

[0002] Especially in the case of drink bottles, in order to be able toreuse the PET even after use of the bottles and/or contamination of thebottles, processes have been developed in the prior art which enablerecycling of polyester. After this recycling the cleaned ordecontaminated polyester or PET can be reused for manufacturing drinkbottles, for example.

[0003] Such processes are disclosed, for example, in PCT/US99/23206. Inthese known processes the PET to be recycled is first comminuted intosmall flakes. The comminuted PET is then placed in water in order to beable to separate lighter materials, such as paper and the like, from thePET by skimming them off from the water surface. The PET is then driedby the action of heat. After drying, the treated PET is mixed with analkaline material. This mixture is also dried by heat. In the subsequentcentral reaction step, the PET which has been mixed with alkalinematerial and dried in this manner is partially saponified with constantfurther drying under the action of heat. The reaction products producedby the saponification are then separated, as a result of which cleanedPET is also produced.

[0004] In order to obtain a satisfactory yield of recycled PET by theabove-mentioned process, it is necessary that the central reaction steptakes place essentially in an anhydrous environment. The rotary furnaceswhich are used for this central reaction step and which are known fromthe prior art, for example the Rotary Calciner, from Heyl & PattersonInc., however, are only able to provide such conditions withrestrictions.

[0005] It is therefore an object of the present invention to improve anapparatus of the type mentioned at the outset, in particular to developit in such a manner that this is able to provide an essentiallyanhydrous environment for carrying out such processes.

[0006] This object is achieved according to the invention by anapparatus according to claim 1.

[0007] The advantages of the invention are, in particular, that the weirinside the rotary tubular furnace which at least in part closes theinterior of the rotary tubular furnace ensures a constant residence timeof the mixture in the rotary tubular furnace, which residence time isindependent of the throughput of the rotary tubular furnace. This inturn means that the mixture always reacts in the rotary tubular furnaceunder the same process parameters, such as temperature and degree ofdryness. Thus, at any throughput rate, the process parameters necessaryfor the maximum yield of recycled polyester can be maintained.

[0008] It is advantageous if the weir is disposed in the region of thedownstream end of the heated furnace region. Here, the action of theweir comes optimally into effect, since the entire length of the heatedregion of the rotary tubular furnace is affected.

[0009] It is advantageous if the weir has, preferably 10 to 14, furtherpreferably 12, star-shaped through holes starting from the center of theweir. In this manner it is possible to define the through hole crosssection for the mixture.

[0010] Preferably, the through holes can at least be partly covered withcovers in order to vary the degree of charging of the rotary tubularfurnace by varying the damming action of the weir, preferably in 5%increments of the degree of charging from 0% to about 30%, furtherpreferably up to 50%. This embodiment guarantees maximum flexibility ofthe rotary tubular furnace and thus optimum adaptation of the dammingaction of the weir to the amount and type of mixture. The through holesor else other perforations in the weir also prevent salts formed in themixture as a result of the saponification from building up excessivelyat the weir and thus impeding the reaction and/or the removal of thereaction products.

[0011] It is particularly preferred if the rotary tubular furnace formsin its interior an essentially cylindrical hollow space for receivingthe mixture. Preferably here the rotary tubular furnace has on its innersurface at least one axially oriented strip. These strips make anessential contribution to improving the rotary tubular furnace withrespect to furnaces of the prior art. These strips prevent the mixturefrom toppling over in the rotary tubular furnace. In this case PETregrind, for example, is present in the mixture in solid form. On theregrind is situated sodium hydroxide solutions which has been dried ontoor into the surface. During reaction of the regrind with the sodiumhydroxide solution, these two reagents form two further byproducts, asalt in solid form and ethylene glycol in gaseous form. On rotation ofthe furnace, this mixture has the tendency to topple over in thefurnace. The toppling over of the mixture in the furnace releases dustwhich forms as a result of the regrind particles rubbing together. Thisdust development known from the prior art is, however, verydisadvantageous for the reasons explained hereinafter.

[0012] The continuous removal of water in the rotary tubular furnaceproduces a moisture gradient in the rotary tubular furnace; at thestart, that is to say at about the height of the product intake, themoisture is higher than at the end of the rotary tube, that is to say atabout the height of the product outlet. The dust formation behaves inthe opposite manner to this course in the rotary tubular furnace. Ifhighly dehydrated dust is swirled up at the end of the furnace, this istransported forward by the passage of exhaust air. The dust reacts withthe sodium hydroxide solution and carries this out via the passage ofexhaust air, since water is absorbed by the dust. Overall the surfacereaction of the alkaline material on the polyester is attenuated, sincethis reaction only proceeds optimally without water, which gives rise,in turn, to complaints of disadvantageous decrease in the yield ofcleaned polyester.

[0013] The inventive strips, however, prevent the toppling over of themixture and thus eliminate the water absorption or absorption of sodiumhydroxide solution by the dust in the furnace and thus increase theyield of cleaned material.

[0014] Advantageously, 5 to 20, preferably 12, uniformly distributedaxial strips are provided along the periphery. Thus toppling over of themixture is constantly prevented over the entire inner periphery.

[0015] It is further advantageous if the at least one axially orientedstrip extends radially inward into the interior of the rotary tubularfurnace in such a manner that in the entire speed range of the rotarytubular furnace toppling over of the mixture in the rotary tubularfurnace is reliably prevented.

[0016] Advantageously, the rotary tubular furnace has a diameter of 2 mto 4 m, preferably 2.6 m, and a heated length of 15 m to 25 m,preferably 18 m. In this manner the required reaction times of more than2 hours may be effected.

[0017] Preferably, the rotary tubular furnace has, to receive themixture, a mixture intake cylinder having a diameter of 0.5 m to 1.5 m,preferably 0.8 m. It is advantageous here if the rotary tubular furnacehas, to deliver the mixture, a mixture outlet cylinder having a diameterof 1 m to 3 m, preferably 1.8 m. Both dimensions fit, in particular,with the above overall furnace length.

[0018] Preferably, the mixture intake cylinder and/or the mixture outletcylinder is connected to the rotary tubular furnace via a conicalpassage.

[0019] It is advantageous if the rotary tubular furnace has, within themixture outlet cylinder, forced transporting elements, for exampletransport spirals, for transporting the mixture, in order to preventmaterial blockage in the case of an advantageous tapering of the tube inthe region of the seal of the mixture outlet cylinder and to guaranteeuniform transport of the mixture.

[0020] Preferably, at the ends of the mixture intake cylinder and/or themixture outlet cylinder, flanges are disposed for receiving seals forairtight sealing of the furnace. These seals are particularly important,since they prevent water or moisture from passing into the furnace. Theytherefore likewise increase the yield. The seal is particularlyimportant at the outlet, since there, in the event of moisture ingress,depolymerization of the product would occur.

[0021] Preferably, the rotary tubular furnace has, in its interior,preferably about six scoop pockets which transport the product up to theoutlet side cone into the mixture outlet cylinder, in particular whensmooth forced transport occurs.

[0022] It is advantageous if the rotary tubular furnace, for mechanicaltransport of the mixture, has an inclination to the horizontal. Theinclination also at least ensures transport of the mixture through thefurnace.

[0023] It is advantageous if the rotary tubular furnace has a hingebearing at its outlet end, so that the rotary tubular furnace can beswung into the inclination by lifting the rotary tubular furnace on theinlet side and pivoting the rotary tubular furnace about this hingebearing.

[0024] Preferably, the inclination is 10 mm/m to 20 mm/m, preferably 15mm/m. At these values of inclination the optimum mixture velocity in thefurnace is achieved.

[0025] Preference is given to providing, within the rotary tubularfurnace, preferably 5 to 20, further preferably 10, thermocouples formonitoring the mixture temperature in the rotary tubular furnace, whichthermocouples are fastened to a measuring beam which is stationaryrelative to the rotary tubular furnace, within the rotary tubularfurnace. By this means the desired reaction temperature in the furnacecan be exactly monitored and, if appropriate, controlled.

[0026] Preferably, two thermocouples are provided per heating zone.Individual control for each heating element is then possible.

[0027] It is advantageous if, at an axial point of the rotary tubularfurnace, in each case two thermocouples are provided which are providedat different distances to the axis of rotation of the rotary tubularfurnace within the rotary tubular furnace. This grid-like arrangement ofthe sensors in the furnace permits monitoring of the temperature atvarious depths of the reacting mixture, since the thermocouples extendinto the mixture to different depths.

[0028] It is advantageous if the rotary tubular furnace has 2 to 5,preferably 3, process zones along its longitudinal axis. By this meansvarious process steps may be completed in one furnace.

[0029] It is advantageous if the design, length and temperature of thefirst process zone are such that further predrying of the mixture can beperformed, preferably from 0.8% to 0.2%, preferably 0.4, water contentto 100 ppm to 50 ppm, preferably 80 ppm, water content.

[0030] Preferably, the design, length and temperature of the secondprocess zone are such that a surface reaction takes place for partialsaponification of the mixture.

[0031] It is advantageous if the design, length and temperature of thethird process zone are such that a diffusion reaction takes place forremoving aromatic contaminants in the mixture.

[0032] Preferably, at least three, preferably five, further preferablyequal-length, heating zones are provided in the rotary tubular furnace.By this means, for each furnace section, the desired temperature in thefurnace can be set very accurately.

[0033] It is advantageous if heating radiators are provided outside therotary tubular furnace, using which the rotary tubular furnace can beheated externally, so that indirect heating of the mixture can beproduced in the rotary tubular furnace.

[0034] Preferably, the rotary tubular furnace has a hot air orifice forthe inflow of hot air into the interior of the rotary tubular furnace,and preferably has a second orifice for the outflow of the used hot air.

[0035] Preferably a hot-air generator is provided for generating the hotair, the temperature of which essentially corresponds to the temperaturein the interior of the heated rotary tubular furnace. In this manner atemperature drop on entry of the air into the interior of the furnace isavoided.

[0036] Preferably, a hot-air drier is provided for drying the hot airprovided for the interior of the rotary tubular furnace. Thus, the hotair also cannot carry any harmful moisture into the furnace.

[0037] It is advantageous if, in the rotary tubular furnace, acountercurrent airflow preferably consisting of hot air, furtherpreferably consisting of dry hot air, can be produced by means of a fanin the opposite direction to the direction of motion of the mixture. Byinstalling the fan in such a manner that the air flows in the oppositedirection to the motion of the mixture in the furnace, constantlymaximally clean and dry hot air arrives at the end section of thefurnace already comprising cleaned polyester, so that this valuableproduct is optimally protected against moisture effects.

[0038] It is advantageous if a mixer is provided for mixing the mixturebefore entry into the rotary tubular furnace, which mixer preferably hasa heated mixing screw. In this manner also a temperature drop of themixture on entry into the furnace is prevented.

[0039] It is advantageous if, upstream of the mixer, a predrier isprovided for drying the polyester provided for the mixer. This alsoprevents the entry of harmful moisture into the furnace.

[0040] It is advantageous if the heating output of the predrier fordrying the contents of the predrier is greater than the aerating outputof the predrier for drying the contents of the predrier. This preventsunreacted sodium hydroxide solution from being removed.

[0041] It is advantageous if, in the predrier, a countercurrent airflowcan be produced in the opposite direction to the direction of motion ofthe material to be dried in the predrier.

[0042] Further preferred exemplary embodiments of the invention aredescribed in the subclaims.

[0043] An exemplary embodiment of the inventive apparatus will now bedescribed with reference to the drawing.

[0044] In the drawing:

[0045]FIG. 1 shows a side view of a rotary tubular furnace;

[0046]FIG. 2 shows the weir of the rotary tubular furnace of FIG. 1 in afront view;

[0047]FIG. 3 shows a diagrammatic side view of the apparatus having therotary tubular furnace of FIG. 1;

[0048]FIG. 4 shows the view of FIG. 1 together with diagrammaticallyrepresented thermocouples;

[0049]FIG. 5 shows a detail of two thermocouples of a heating zone;

[0050]FIG. 6 shows a diagrammatic detail of the strips in the rotarytubular furnace of FIG. 1;

[0051]FIG. 7 shows a diagrammatic detail of orifices in the rotarytubular furnace of FIG. 1; and

[0052]FIG. 8 shows a diagrammatic detail of brushes in the rotarytubular furnace of FIG. 1.

[0053]FIG. 1 shows a side view of a rotary tubular furnace 1. The rotarytubular furnace 1 has a cylindrical shell 3 and is mounted so as to beable to rotate on bearings which are not shown by means of running rings6 and 8 provided in the region of its ends 2 and 4, respectively. Theshell 3 surrounds a product space 5 for receiving the mixture to betreated, which is not shown.

[0054] The end 4 forms the outlet-side end and the end 2 forms theinlet-side end of the rotary tubular furnace 1. The rotary tubularfurnace 1 can be driven via a toothed ring 10 provided in the region ofthe end 4, which toothed ring is driven by a toothed ring pinion 12driven by a motor which is not shown. The rotary speed of the rotarytubular furnace 1 may be set between 0.5 and 5.0 rpm.

[0055] On the inlet side, the end 2 has a coaxial cylindrical extension14. This serves the rotary tubular furnace 1 as mixture intake for themixture. The extension 14 has a smaller diameter than the shell 3 and isconnected to the shell 3 via a conical connection piece 16.

[0056] On the outlet side the end 4 likewise has a coaxial cylindricalextension 18. This serves the rotary tubular furnace 1 as mixture outletfor the recycled mixture. The extension 18 has a smaller diameter thanthe shell 3, but a greater diameter than the inlet-side extension 14,and is connected to the shell 3 via a conical connection piece 20 which,owing to the smaller difference in diameter compared with the inlet sidebetween the extension 18 and the shell 3, at the same gradient isshorter than the connection piece 16 at the end 2.

[0057] In the region of the outlet-side end 4, but, in the direction ofmotion of the mixture, still upstream of the connection piece 20, astar-shaped weir 22 is provided. This weir 22 extends radially from theaxis of rotation 24 of the rotary tubular furnace 1 from the interior tothe shell 3. In the weir 22 are provided through holes 26 for themixture.

[0058]FIG. 2 shows the weir 22 of the rotary tubular furnace 1 of FIG. 1in a front view. FIG. 2 shows twelve through holes 26 in the weir 22which leave in a star shape from a closed central region 28. Theorifices 26 may be individually closed using the covering sheets 30.

[0059]FIG. 3 shows a diagrammatic side view of the apparatus 100 havingthe rotary tubular furnace 1 of FIG. 1. Parts which correspond to thoseof FIGS. 1 and 2 are identified with the same reference numbers.

[0060] Furthermore, FIG. 3 shows the following:

[0061] a heating tunnel 32 enclosing the rotary tubular furnace 1 andhaving an electrical heating device 34, which heating tunnel axiallysurrounds the furnace shell 3. The heating tunnel 32 does not rotate inconjunction and is fitted with 5 separately controllable heating zones36. Each heating zone 36 has a separate heat radiator 49 whichirradiates the shell 3 of the rotary tubular furnace 1 externally withheat.

[0062] Intake 38 and outlet 40 housings, each of which close off theends of the product space 5 (formed by the furnace shell 3). Bothhousings 38 and 40 are stationary.

[0063] Inlet- and outlet-side Burgmann seals 42 and 44 which seal offthe product space 5 between the rotating furnace shell 3 and thestationary inlet- and outlet-housings 38 and 40.

[0064] Instruments for measuring the product temperatures 46 and theshell temperatures 48, each present for each temperature control zone36. The instruments for measuring the product temperatures and mixturetemperatures have stationary thermocouples 50 in the product space. Ineach case two thermocouples 50 are provided per heating zone 36.

[0065]FIG. 4 shows the view of FIG. 1 with diagrammatically representedthermocouples 50. The thermocouples are fixed to a central measuringbeam 52.

[0066]FIG. 5 shows a detail view of two thermocouples 50 of a heatingzone 36. It may be seen that the two thermocouples 50 a and 50 b are atdifferent distances from the central measuring beam 52, so that theyextend to a different extent into the mixture.

[0067]FIG. 6 shows a diagrammatic detail of strips 60 in the rotarytubular furnace 1 of FIG. 1. The furnace 1 rotates in accordance witharrow 62. The strips 60 prevent the mixture 64 from toppling over duringrotation of the rotary tubular furnace 1. During rotation of the rotarytubular furnace 1, the mixture 54 rather, because of the strips 60,always slides back in accordance with arrow 66, without toppling over.

[0068] The mode of operation of the rotary tubular furnace 1 shown isdescribed hereinafter. This mode of operation forms a part of thepresent invention. The direction of claims toward the details of thismode of operation is reserved here.

[0069] The indirectly heated rotary tubular furnace 1 serves forreprocessing the mixture 64 (here recycled PET regrind), which isrecirculated to the product space 5 in the predried state (residualmoisture max. 0.4% by mass of water). The feed material additionallycontains NaOH (max. 10% by mass of 50% strength NaOH), which reacts withthe PET on the surface under the temperature conditions in the rotarytubular furnace 1—PET granules are formed which, after further processsteps, are again suitable for producing food packaging. The approval forthe use in food packages is connected to the fact that the PET residencetime above 400 K is at least 2 hours.

[0070] During start-up of the furnace 1, the star weir 22 should firstlybe adapted to the processing conditions. For this it is important toknow that the function of maintaining constancy of the product residencetime (in the heatable furnace region) is achieved independently ofproduct throughput rate only in an absolutely ideal manner provided thatthe mechanical product behavior and also furnace rotary speed andfurnace inclination are kept constant. The mechanical product behaviorwill essentially remain constant (independently of the throughput rate),if the particle size distribution and the global particle shape of thePET regrind do not change. The star weir 22 is set by opening or closingthe parabolic through holes 26 in the star weir 22—for this the closuresheets 30 which can be screwed in are provided for in total 12 orifices26.

[0071] The adjustment operations should be carried out in the coldfurnace state, preferably according to the following plan:

[0072] Start with six open holes 26, the preferred furnace speed ofrotation (proposed 4 min⁻¹) and fixed (for example half) throughput rateof representative feed material.

[0073] Wait for the steady-state operating state (10-15 hours) andmonitor the product charging state at the star weir 22 with the furnace1 stationary. It is presumed that the charging state existing at thisfirst monitoring may not yet correspond to the preset charging state forthe chosen throughput rate. If it is too low, some holes 26 must beclosed; if it is too high, further holes 26 must be opened—theappropriate number must be determined by calculation using a simple ruleof three.

[0074] Restart the furnace drive and product feed at the above-selectedsettings. After waiting again for the steady-state operating state(about 10 hours), again check the product charge state at the star weir22 with furnace 1 stationary—now the preset and actual values shouldagree (if not a repeated adaptation is necessary).

[0075] If it is considered necessary, this can be followed by checkingas to whether the conditions are correct even under changed throughputrates.

[0076] It can likewise be expedient to check the effect of a variationin speed of rotation, so that any inadequacies present in the functionof the star weir 22 (for example in the event of a changed particle sizedistribution as a function of the throughput rate) can be compensatedfor a by a (slight) adaptation rotary speed.

[0077] Should at some time a general change in product quality arise,the star weir 22 is to be readjusted for this product—the same appliesin the event of a general change in standard furnace speed of rotationor up to a change in furnace inclination.

[0078] After the adjustment procedures to the star weir 22 have beencompleted (and if appropriate the furnace 1 has been run completelyempty), heating up can be started.

[0079] For this the following information is of importance:

[0080] For monitoring, the following are available for each temperaturecontrol zone 36, one radiation pyrometer 48 for contact-free measurementof the drum wall temperature, two double thermocouples 50 for measuringthe product temperature (700 mm and 200 mm distance from the drum wall3) and a plurality of double thermocouples for over temperaturemonitoring of the electrical heating elements.

[0081] The product temperature is measured (as described above) at twodifferent distances from the drum wall 3, that is to say one×high in theproduct bed and one×deep in the product bed. The deep measuring pointsare always in contact with product provided that the degree of furnacecharge is above 3.5%; in the case of the high measuring points this isonly the case at charge degrees greater than 21.5%. It may be noted thatthe high measuring points in part do not indicate the producttemperature, but the gas temperature.

[0082] The heating power for each temperature control zone can be setsteplessly from zero to a maximum, preferably individually matched tothe respective requirements. The respective heating power is controlledautomatically via inputting the preset drum shell temperature for eachcontrol zone 36 and measuring the actual drum shell temperature by theradiation pyrometer 48.

[0083] The heating power is in each case restricted by monitoring themaximum permissible heating element temperature by means of theabove-mentioned double thermocouples.

[0084] In selection of the drum wall temperatures, it must be noted thatPET has a melting point of approximately 250° C. (lower values are alsopossible as a result of impurities). Practical and theoretical studieshave found that for product temperatures less than 180° C., drum shelltemperatures up to a maximum of 280° C. can be employed without meltingof product in the drum shell 3 occurring—however, a condition for thisis a sufficiently rapid mixing of the product 64; it is thereforerecommended to employ a drum speed of at least 4 min⁻¹. Above a producttemperature of 180° C., the drum wall temperature should be set belowthe melting point (that is to say less than 250°); above a producttemperature of 220° C., the wall temperature, for safety, should bedecreased to <230° C. (because of a possible lower melting point due toimpurities in the PET). The displays of the low measuring points (seeabove) should always be used as a basis for the index of the relevantproduct temperatures in this case.

[0085] To avoid hydrolysis of the PET at high temperatures, dried (andpreheated to 220° C.) hot air is passed through the product space 5—sothat the residual moisture vaporized in the inlet region does not comeinto contact with the further heated PET in the outlet region, the airis passed through the furnace 1 in countercurrent to the product. Inthis context, particular importance is ascribed to the Burgmann sealswhich form the transition between the rotating rotary furnace shell 3and the stationary intake and outlet housings 38 and 40. Attempts shouldbe made to prevent, at these points, ambient air from entering into theproduct space 5, or dust and gases from the furnace 1 from escaping. Inorder that this can be reliably ensured, the Burgmann seals shouldlikewise be exposed to dried (and preheated to 220° C.) air. The inletpressure of this air feed should be chosen to be high enough that noprocess gases are forced into the Burgmann seal and that dust is keptaway from the seal surfaces (“blown off”)—in principle this can beimplemented most simply and reliably if the product space 5 is kept at aslight reduced pressure (−0.1 to −1 mbar). It is desirable to restrictthe volumetric flow rate of the air charge—control of this is providedin each case by means of an on-site volumetric flow display and acontrol valve.

[0086] In the event of loss of the main furnace drive (for example dueto damage to the motor or a power outage), care should be taken for thisthat (provided that the furnace shell 3 is hot) an emergency drive isused (for example auxiliary motor on emergency power busbar) and thatthe heating device 49 is turned off.

[0087] The (slow) continued rotation of the furnace 1 is required toprevent sticking of the product to the furnace shell. These measures arepreferably part of a plant interlock system and should proceedautomatically.

[0088]FIG. 7 shows a diagrammatic detail of orifices 80 in the rotarytubular furnace 1 of FIG. 1. The orifices 80 lead to the outsidetransversely to the axis through the shell 3. The hollow space 5 has asecond weir 82 adjacent to the orifice 80. The second weir 82 isdisposed upstream of the orifice 80. The second weir 82 has a throughhole 84 which is disposed adjacently to the orifice 80 and adjacent tothe outer wall 3 of the hollow cavity 5.

[0089] In addition, a deflection means 86 is provided which isconstructed as sheet metal and directing at least temporarilyessentially to the orifice 80. The sheet metal 86 pivots under the forceof gravity about a pivot axis 88, the pivot axis 88 being disposed atthe second weir 82 in such a manner that the sheet metal 86 downstreambehind the through hole 84 only leads to the orifice 80 when the hollowspace 5, on rotation of the rotary tubular furnace 1, is in the lowerdead point of a rotation. This is indicated in the lower part of FIG. 7.

[0090] In addition, the orifice 80 is covered at least in part by ascreen 90 serving as screen device, the orifice 80 leading to acollection device 92 for material entering through the orifice 80.

[0091] The functioning of the orifice 80 is as follows:

[0092] If material is situated in the lower region of the rotary tubularfurnace 1, the flap 86 is closed by the force of gravity. Coarse-grainedmaterial passes over the weir 82 and separated fine-grain material,which is termed undersize grain, passes through the lower orifices 82 tothe outside. After exit of the fine-grained material, there is ascreening through the screen layer 90 mounted in a ring shape on thefurnace periphery 3. The screen layer 90 need not absolutely be porous.The undersize grain of this screen is separated by the collection device92. The undersize grain remaining on the screen coat 90 is transportedin conjunction with the material passing by. The orifice 80 thereforeoffers the possibility of separating off undersize grain by installationof the upstream smaller weirs 82. If PET is to be cleaned using therotary tubular furnace 1, the undersize grain is salts and PET fineswhich can be separated off thanks to the orifices, which increases thequality of the end product.

[0093]FIG. 8 shows a diagrammatic detail view of brushes 90 in therotary tubular furnace 1 of FIG. 1. The transition 20 between rotarytubular furnace 1 and mixture outlet cylinder 18 has two brushes 90 forbrushing off material penetrating the transition 20. The brushes 90prevent dusts from depositing at this point, since dusts penetrating tothe seal 92 between mixture outlet cylinder 18 and rotary tube 1 areconstantly brushed off. The brushes 90 are turned in such a manner thatmaterial penetrating into the transition 20 is brushed back to themixture outlet cylinder 18, away from a seal 92, that is to say into themixture outlet cylinder 18. From there, the dusts can be dischargedeither by the air extractor or together with the material flow.

1. An apparatus for cleaning and/or decontaminating polyester, having anat least partially heated rotary tubular furnace (1) to be fed with amixture (64) of polyester and an alkaline material and for carrying outa saponification reaction in the mixture (64), in which at least oneweir (22) is arranged within the rotary tubular furnace (1), which weirat least partly closes the interior (5) of the rotary tubular furnace(1), wherein the weir (22) has at least one through hole (26) which canat least be partly closed using a closure (30) in order to vary thedegree of charge of the rotary tubular furnace (1) by varying thedamming action of the weir (22).
 2. The apparatus as claimed in claim 1,wherein the weir (22) is disposed in the region of the downstream end ofthe heated furnace region.
 3. The apparatus as claimed in one of thepreceding claims, wherein the weir (22) has, preferably 10 to 14,further preferably 12, through holes (26) leaving in a star shape fromthe center of the weir (22).
 4. The apparatus as claimed in thepreceding claim, wherein the through holes (26) can be covered at leastin part by the covering (30) in such a manner that they vary the degreeof charge of the rotary tubular furnace by varying the damming action ofthe weir in 5% increments of the degree of charge from 0% to about 30%,preferably to about 50%.
 5. The apparatus as claimed in one of thepreceding claims, wherein the at least one cover (30) has an irisdiaphragm.
 6. The apparatus as claimed in the preceding claim, whereinthe iris diaphragm can be set steplessly.
 7. The apparatus as claimed inone of the two preceding claims, wherein the iris diaphragm can be setfrom outside the rotary tubular furnace (1).
 8. The apparatus as claimedin one of the preceding claims, wherein the rotary tubular furnace (1)forms, in its interior, an essentially cylindrical hollow space (5) forreceiving the mixture (64).
 9. The apparatus as claimed in the precedingclaim, wherein the hollow space (5) has at least one orifice (80) whichleads to the exterior essentially transversely to the axis.
 10. Theapparatus as claimed in the preceding claim, wherein the hollow space(5) has at least one second weir (82) disposed essentially adjacently tothe orifice (80).
 11. The apparatus as claimed in the preceding claim,wherein the second weir (82) is disposed essentially upstream of theorifice (80).
 12. The apparatus as claimed in the preceding claim,wherein the second weir (82) has a through hole (84) disposedessentially adjacently to the orifice (80), preferably also adjacentlyto an outer wall (3) of the hollow space (5).
 13. The apparatus asclaimed in one of claims 9-12, wherein a deflecting means (86) leadingat least temporarily essentially to the orifice (80) is provided. 14.The apparatus as claimed in the preceding claim, wherein the deflectingmeans (86) leads to the orifice (80) essentially only in the lower deadpoint of a revolution of the hollow space (5).
 15. The apparatus asclaimed in the preceding claim, wherein the deflecting means (86) canpivot about a pivot axis (88), preferably under the force of gravity.16. The apparatus as claimed in claim 12 and as claimed in the precedingclaim, wherein the pivot axis (88) is disposed at the second weir (82)in such a manner that the deflecting means (86) downstream of thethrough hole (84) essentially only leads to the orifice (80) when thehollow space (5) is in the lower dead point of a revolution.
 17. Theapparatus as claimed in one of claims 9-16, wherein the orifice (80) iscovered at least in part by a screen device (90).
 18. The apparatus asclaimed in one of claims 9-17, wherein the orifice (80) leads to acollection device (92) for material passing through the orifice (80).19. The apparatus as claimed in one of the preceding claims, wherein therotary tubular furnace (1) has, on its inner surface, at least oneaxially oriented strip (60).
 20. The apparatus as claimed in thepreceding claim, wherein 5 to 20, preferably 12, axial strips (60)uniformly distributed along the periphery are provided.
 21. Theapparatus as claimed in one of claims 8, 19 or 20, wherein the at leastone axially oriented strip (60) extends radially inward in the interior(5) of the rotary tubular furnace (1) to a sufficient extent that in theentire rotary speed range of the rotary tubular furnace (1), the mixture(64) is prevented from toppling over into the rotary tubular furnace(1).
 22. The apparatus as claimed in one of the preceding claims,wherein the rotary tubular furnace (1) has a diameter of 2 m to 4 m,preferably 2.6 m, and a heated length of 15 m to 25 m, preferably 18 m.23. The apparatus as claimed in one of the preceding claims, wherein therotary tubular furnace (1) has, to receive the mixture (64), a mixtureintake cylinder having a diameter of 0.5 m to 1.5 m, preferably 0.8 m.24. The apparatus as claimed in one of the preceding claims, wherein therotary tubular furnace (1) has, to deliver the mixture (64) a mixtureoutlet cylinder (18) having a diameter of 1 m to 3 m, preferably 1.8 m.25. The apparatus as claimed in one of claims 23 or 24, wherein themixture intake cylinder (14) and/or the mixture outlet cylinder (18)having a preferably conical transition (16; 20) is connected to therotary tubular furnace (1), preferably via a seal (98).
 26. Theapparatus as claimed in the preceding claim, wherein the transition (16;20) between rotary tubular furnace (1) and mixture intake cylinder (14)and/or mixture outlet cylinder (18) has at least one brush means (96)for brushing off material penetrating into the transition (16; 20). 27.The apparatus as claimed in the preceding claim, wherein the brush meanshas at least one cleaning element, preferably a cleaning elementcomprising brushes (96), which element is constructed in such a mannerthat material penetrating into the transition (16; 20) is transportedback into the mixture intake cylinder (14) and/or the mixture outletcylinder (18), preferably away from the seal (98).
 28. The apparatus asclaimed in one of the preceding claims, wherein the rotary tubularfurnace (1) has, within the mixture outlet cylinder (18) transportspirals for transporting the mixture (64).
 29. The apparatus as claimedin one of the preceding claims, wherein, at the ends of the mixtureintake cylinder (14) and/or the mixture outlet cylinder (18), flangesare disposed for receiving seals for the air-tight sealing of the rotarytubular furnace (1).
 30. The apparatus as claimed in one of thepreceding claims, wherein the rotary tubular furnace (1), in itsinterior, has, preferably about 6, scoop pockets which transport theproduct up the outlet-side cone into the mixture outlet cylinder (18).31. The apparatus as claimed in one of the preceding claims, wherein therotary tubular furnace (1), for the mechanical transport of the mixture(64), has an inclination to the horizontal.
 32. The apparatus as claimedin one of the preceding claims, wherein the rotary tubular furnace (1)has, at an outlet-side end, a hinge bearing, so that the rotary tubularfurnace (1) can be swung into the inclination by inlet-side elevationand pivoting the rotary tubular furnace (1) about this hinge bearing.33. The apparatus as claimed in one of the preceding claims, wherein theinclination is 10 mm/m to 20 mm/m, preferably 15 mm/m.
 34. The apparatusas claimed in one of the preceding claims, wherein, within the rotarytubular furnace (1), preferably 5 to 20, further preferably 10,thermocouples (50, 50 a, 50 b) are provided for monitoring the mixturetemperature in the rotary tubular furnace (1), which thermocouples arefixed to a measuring beam (52) which is stationary relatively to therotary tubular furnace (1) and is within the rotary tubular furnace (1).35. The apparatus as claimed in the preceding claim, wherein twothermocouples (50, 50 a, 50 b) are provided per heating zone (36). 36.The apparatus as claimed in one of the preceding claims, wherein, at anaxial point of the rotary tubular furnace (1), in each case twothermocouples (50, 50 a, 50 b) are provided, which are provided withinthe rotary tubular furnace (1) at different distances to the axis ofrotation (24) of the rotary tubular furnace (1).
 37. The apparatus asclaimed in one of the preceding claims, wherein the rotary tubularfurnace (1) has 2 to 5, preferably 3, process zones along itslongitudinal axis (24).
 38. The apparatus as claimed in the precedingclaim, wherein the design, length and temperature of the first processzone are such that a further predrying of the mixture (64) can beperformed, preferably from 0.8% to 0.2%, preferably 0.4%, water contentto 100 ppm to 50 ppm, preferably 80 ppm, water content.
 39. Theapparatus as claimed in one of the two preceding claims, wherein thedesign, length and temperature of the second process zone are such thata surface reaction takes place for the partial saponification of themixture (64).
 40. The apparatus as claimed in one of the three precedingclaims, wherein the design, length and temperature of the third processzone (64) are such that a diffusion reaction takes place to removearomatic impurities in the mixture (64).
 41. The apparatus as claimed inone of the preceding claims, wherein, in the rotary tubular furnace (1),at least three, preferably five, further preferably equal-length,heating zones (36) are provided.
 42. The apparatus as claimed in one ofthe preceding claims, wherein heating radiators (49) are providedoutside the rotary tubular furnace (1), using which the rotary tubularfurnace (1) can be heated externally, so that indirect heating of themixture (64) in the rotary tubular furnace (1) can be produced.
 43. Theapparatus as claimed in one of the preceding claims, wherein the rotarytubular furnace (1) has a hot-air orifice (70) for the inflow of hot airinto the interior of the rotary tubular furnace (1), and preferably asecond orifice (72) for the outflow of the used hot air.
 44. Theapparatus as claimed in the preceding claim, wherein a hot-air produceris provided for producing the hot air, the temperature of whichessentially corresponds to the temperature in the interior of the heatedrotary tubular furnace (1).
 45. The apparatus as claimed in one of thepreceding claims, wherein a hot-air drier is provided for drying the hotair provided for the interior of the rotary tubular furnace (1).
 46. Theapparatus as claimed in one of the preceding claims, wherein, in therotary tubular furnace (1), a countercurrent air flow preferablyconsisting of hot air, further preferably of dry hot air, can beproduced using a fan in the opposite direction to the direction ofmotion of the mixture.
 47. The apparatus as claimed in one of thepreceding claims, wherein a mixer (74) is provided for mixing themixture prior to entry into the rotary tubular furnace (1), which mixer(74) preferably has a heated mixing screw (76).
 48. The apparatus asclaimed in the preceding claim, wherein a predrier is provided upstreamof the mixer (74) for drying the polyester provided for the mixer (74).49. The apparatus as claimed in the preceding claim, wherein the heatingoutput of the predrier for drying the contents of the predrier isgreater than the aerating power of the predrier for drying the contentsof the predrier.
 50. The apparatus as claimed in one of the twopreceding claims, wherein a countercurrent airflow can be produced inthe predrier in the opposite direction to the direction of motion of thegoods to be dried in the predrier.